The Yankees alleged their bitter rival was using Apple Watches to steal signs, in violation of baseball rules. The Red Sox said the Yankees were doing something similar.

The decades-old rivalry between the New York Yankees and Boston Red Sox is filled with beanballs, brawls and lots and lots of yelling. Now a modern weapon has been introduced to Yankees-Red Sox lore: the Apple Watch.

Major League Baseball commissioner Rob Manfred said Tuesday that the league is investigating the Red Sox for concocting an elaborate process to use an Apple Watch for the purpose of stealing signs.